Certain diesel engines that power motor vehicles use a fixed displacement type oil pump to deliver oil under pressure to an oil rail that serves electric-actuated fuel injectors. Because that type of pump is prone to associated accessory or parasitic losses that are greater than losses associated with a variable displacement type pump, use of the latter type pump should be preferred so that increased operating efficiencies can be obtained. Brake Specific Fuel Consumption (BSFC) of the engine and hence vehicle fuel economy may be improved as a result.
However, successful use of such a pump requires an appropriate control strategy. It is toward providing such a strategy that the present invention is directed.
One known type of variable displacement pump has two pumping stages. It is sometimes called a two-stage, or dual-stage, pump. Each of the two stages pumps oil independently of the other. By employing a two-stage, variable displacement pump as an oil pump in a diesel engine, a particular control strategy for selecting and de-selecting each stage forms an important element of an overall strategy for controlling flow and pressure of oil pumped to an oil rail that serves the fuel injectors. This enables the oil system to operate in a more efficient manner over a full range of engine operating conditions than one having a fixed displacement pump.
In the disclosed exemplary embodiments of the present invention, electric-controlled flow control valves are associated with each stage of the two-stage, variable displacement oil pump and are under control of the engine control system to control the shunting of pumped oil away from the oil rail and into a sump from whence the oil returns to an oil reservoir from which the pump draws oil.
When a stage is de-selected by a stage selection control strategy, the corresponding valve is maximally open to shunt the entire flow from that stage to the sump so that the stage makes no contribution to the oil being pumped to the oil rail. When a stage is selected, the corresponding valve is controlled in a manner that controls the extent to which the pumped oil is shunted to the sump.
The pressure at the oil rail is often referred to as injector control pressure, or ICP, and that pressure is under the control of an appropriate ICP control strategy that forms another element of the overall engine control strategy. The two strategies, namely the stage selection control strategy and the ICP control strategy, conjunctively enable the oil rail to provide ICP that is appropriate for engine operation over a full range of operating conditions while doing so in a manner that achieves improved engine efficiency.
An important advantage of the invention is that it provides for automatic transitional control of the flow control valves during the process of selecting a de-selected stage and during the opposite process of de-selecting a selected stage. Two different embodiments of the invention will be disclosed: a first embodiment that comprises two flow control valves, each associated with a respective stage of a two-stage, variable displacement, engine-driven oil pump, and a second embodiment that comprises an additional third flow control valve, associated with a common outlet from the two stages leading to the oil rail. In the two-valve embodiment, the valves are operated by the stage selection strategy in ways that provide gradual, rather than sudden, transitions in valve operation during selection and de-selection processes. In the three-valve embodiment that has the third valve for modulating the combined flows of the two stages, the other two valves that are associated with the respective stages are operated suddenly, rather than gradually.
A known electronic engine control system comprises a processor-based engine controller that processes data from various sources to develop control data for controlling certain functions of the engine. The engine control system controls both the duration and the timing of each fuel injection to set both the amount and the timing of engine fueling. The engine control system is also used to implement the strategy for control of the oil system, implementing both the pump stage selection strategy and the ICP control strategy.
The present invention comprises a strategy for selecting and de-selecting each stage such that at times only one stage is selected and at other times both stages are selected. The strategy for the first embodiment also makes the transition between selecting and de-selecting a stage, and vice versa, gradual, rather than sudden, by gradually operating the corresponding valve from open to closed, and vice versa.
Accordingly a generic aspect of the invention relates to an internal combustion engine comprising a fueling system comprising fuel injectors that utilize pumped hydraulic fluid, (oil being a commonly used hydraulic fluid), to force diesel fuel into engine combustion chambers and a hydraulic system comprising an engine-driven pump for pumping the fluid to the fuel injectors. The effective displacement of the pump can be varied, (stage selection of a multi-stage pump using electric-controlled valves being an example), to control the flow of pumped fluid to the fuel injectors. A control system controls the effective displacement of the pump, thereby controlling the flow of pumped fluid to the fuel injectors.
Each of the two specific embodiments of the invention that will be described comprises a two-stage pump and a control system that is effective to allow either one or both of the stages to pump oil to the fuel injectors and control the oil flow from each stage to the fuel injectors independently of the other stage. In this way, the inventive strategy promotes pumping efficiency for the oil system over a full range of engine operation, thereby avoiding losses that detract from fuel economy.
Another generic aspect relates to an internal combustion engine comprising a fueling system comprising fuel injectors that utilize pumped hydraulic fluid to force fuel into engine combustion chambers. A hydraulic system that comprises a multi-stage pump pumps hydraulic fluid to the fuel injectors. A control system selects and de-selects the pump stages for pumping fluid to the fuel injectors.
Related aspects concern methods for control of the pumped fluid as performed by the engines described above.
The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows.